This application claims the benefit under 35 U.S.C. xc2xa7365 of French patent application No. 0111193 filed Aug. 29, 2001.
The invention pertains to the field of telecommunications and relates to a compact, planar antenna which is made on a substrate in the form of an annular slot, designed to operate at a given frequency, which is placed in a short-circuit plane of a line via which this slot is fed.
It also relates to telecommunications terminals and in particular to the terminals of wireless mobile and domestic networks, where a compact and planar antenna such as this is desired in order to allow a terminal to utilize one and the same polarization on transmission and on reception.
For practical purposes and in order to occupy just a small volume, numerous wireless telecommunications terminals make use of one and the same antenna, made in a compact form, to transmit and receive. In a known form of embodiment, each terminal includes an antenna switch making it possible to link its antenna alternately either to a transmission module, or to a reception module of which it makes use. As is known, the power delivered by a terminal to its antenna within the context of a transmission is markedly greater than that which it receives within the context of a reception. The antenna switch, designed to operate with these different powers, often has the drawback of introducing appreciable losses which degrade the performance of the terminal, both on transmission and in reception, and moreover it has a cost which is relatively high.
A solution utilized within the context of point-to-point links"" makes it possible to avoid the use of an antenna switch, it consists in feeding the antenna of a terminal on two orthogonal polarizations. In one form of embodiment, a first linear and horizontal polarization is used for transmission from a terminal, a second linear and vertical polarization being used in reception. However, this solution necessitates that communicating terminals have dissymmetric antennas, the polarization of a terminal on transmission corresponding to the polarization in reception of the terminal with which it is communicating and vice-versa.
Within the context of wireless telecommunications networks, it is generally desired to retain the same polarization for the transmit and receive pathways of the terminals. This has led to solutions envisaging the use of two antennas per terminal, one for transmission and the other for reception, so as to be able to retain the same polarization.
The invention proposes a compact, planar antenna made on a substrate comprising an annular slot which is dimensioned to operate at a given frequency and which is placed in a short-circuit plane of a linevia which the said antenna slot is fed.
According to a characteristic of the invention, the antenna comprises a second slot feed line which is symmetrically disposed with respect to the other in the said short-circuit plane common to them, each of the feed lines, furnished with a port making it possible to supply the antenna, being connected to a switching facility by way of which this port can be rendered active or passive, so as to allow in particular alternate use of one and the same polarization on the basis of two distinct ports, one for the purposes of transmission and the other for the purposes of reception. The invention also pertains to a telecommunications terminal of the type including an antenna, as well as a rig for transmission and a rig for reception by radio both utilizing the antenna.